1. Field of the Invention
The present invention relates to an image forming apparatus and a control method thereof, and particularly to an image forming apparatus having a file storage function and a control method thereof.
2. Description of the Related Art
Recently, an image forming apparatus such as a digital compound machine (Multi-Function Peripheral) or an image reading apparatus such as a scanner apparatus is often constructed such that a large capacity storage apparatus such as, for example, an HDD (Hard Disk Drive) is incorporated and an image file of a read original document can be stored in this storage apparatus.
The image file stored in the HDD or the like can be read from the HDD or the like and can be printed as required, or can be captured in an information processing apparatus such as a personal computer (PC).
On the other hand, documents to be read by the image forming apparatus or the like include a highly confidential document. In order to prevent illegal access to the highly confidential document or falsification thereof, it is necessary to take security measures at the time of storage into the HDD or the like.
As the security measures taken in the related art, there is an encryption method using an encryption key (common key). This method is such that a highly confidential document is encrypted using the encryption key previously provided to the apparatus, and then is stored in the HDD or the like, and data read from the HDD or the like is also decrypted using this common key.
However, in the related art image forming apparatus, the same encryption key is generally continuously used. Thus, it is impossible to completely preclude the possibility that the encryption key is estimated by analyzing the encrypted document stored for a long period of time. In case the encryption key is estimated, there is a possibility that the confidential document stored in the HDD or the like is decoded or falsified, and the damage at that time is enormous.
In order to improve the security at the time of storage into the HDD of the image forming apparatus or the like, for example, JP-A 2005-34825 discloses a technique in which both a common key and a public key are used. The data encrypted by the common key is stored in the HDD, the common key is encrypted by the public key, and the encrypted common key is also stored in the same HDD. When the data read from the HDD is decrypted, an IC card in which a secret key paired with the public key is stored is inserted in the image forming apparatus, the common key is first decrypted by the secret key, and the data is decrypted by the decrypted common key. According to the technique disclosed in JP-A 2005-34825, although it is certain that the decoding itself of the data becomes difficult, the IC card must be carried at each time of reading from the HDD, which is troublesome in operation, and there occurs a new security problem, such as safekeeping and management of the IC card.